1. Field of the Invention
The present invention relates to a demodulator for demodulating signals including a predetermined modulated signal, a disk drive device including the demodulator, and a demodulation method. For example, the present invention is suitable for demodulation of a minimum shift keying (MSK) modulated signal used as the predetermined modulated signal.
2. Description of the Related Art
Demodulation techniques are disclosed in Japanese Unexamined Patent Application Publication Nos. 11-306686, 2002-74660, 2005-222608, and 2006-12348.
In data recording techniques for recording and reproducing digital data, optical disks (including magneto-optical disks), such as a compact disk (CD), a mini-disk (MD), a digital versatile disk (DVD), are used as recording media.
The optical disks include read-only types, such as, for example, a CD, a CD-ROM (compact disk-read only memory), and a DVD-ROM, and user-data-recordable types, such as an MD, a CD-R (compact disk recordable), a CD-RW (compact disk-rewritable), a DVD-R (DVD recordable), a DVD-RW, DVD+RW, and a DVD-RAM. In the recordable types, a magneto-optical recording method, a phase change recording method, a pigment-layer change recording method, and other recording methods are utilized to record data. The pigment-layer change recording method, also referred to as write-once recording method, is considered suitable for use in data storage because it permits data recording only once. On the other hand, the magneto-optical recording method and the phase change recording method permit data rewriting, thereby finding many applications in the recording of various contents including music, videos, games, and application programs.
Furthermore, recently developed high-density optical disks, called Blu-Ray Discs®, offer an extremely high data storage capacity.
Guides for tracking a data track are required to record data onto recordable disks that work in the magneto-optical recording method, the pigment-layer change recording method, the phase change recording method, or the like. To this end, a groove is formed as a pre-groove, and the groove or a land (an elevated land portion between grooves in cross section) is tracked in data recording.
Address information needs to be recorded to record data at a predetermined location on a data track. The address information may be sometimes recorded by wobbling the groove.
More specifically, the track for recording data is formed as, for example, a pre-groove, and the sidewall of the pre-groove is wobbled in accordance with the address information.
With this configuration, addresses can be read from the wobbling information obtained as reflected laser information during recording and reproducing operations. Data is thus recorded to or reproduced from a target location without the need for previously forming pit data representing the address on tracks, for example.
The address information arranged as the wobbling groove eliminates the need for arranging address areas discretely on the track and recording an address as pit data. As the address area becomes unnecessary, an amount of actual recordable data is increased accordingly.
Absolute time information (address) represented by the wobbled groove is referred to as the absolute time in pregroove (ATIP), or the address in pregroove (ADIP).
In the case of Blu-Ray Disks®, the groove is wobbled in accordance with a modulated waveform that is modulated in a combination of an MSK modulation and a saw tooth wobble (STW) modulation.
The ADIP information, formed using the MSK modulation, the STW modulation, or a combination of both modulations, will be discussed in more detail later. The MSK modulation is one of continuous phase frequency shift keying (FSK) modulations with a modulation index of 0.5.
In the STW modulation, a second harmonic of a wobble fundamental wave is added to or subtracted from the wobble fundamental wave so that a modulated wave, such as a saw-tooth wave, is generated.
A disk drive device for Blu-Ray Disks®, for example, contains an MSK demodulator and an STW demodulator to reproduce the ADIP information.
In particular, techniques for demodulating MSK/STW modulated signals, and decoding the ADIP information are disclosed in Japanese Unexamined Patent Application Publication Nos. 11-306686, 2002-74660, 2005-222608, and 2006-12348.